WASHINGTON, U.S. - The Federal Bureau of Investigation (FBI) has launched an investigation into a cyberattack suffered by members of the U.S. Republican Party.

According to a report in Politico, an official of the National Republican Congressional Committee (NRCC) spotted the hacking of email accounts of some key Republican campaign officials during the month of April, and alerted the committee.

The report noted that the NRCC subsequently discovered that accounts of four senior aides had been targeted and that the accounts were compromised for several months.

However, the U.S. Republican Party officials pointed out that none of the emails had been made public.

The email hacking, which took place ahead of the November mid-term elections, was subsequently reported to the FBI, which began an investigation.

The NRCC, which co-ordinates election campaigns for Republican candidates running for the U.S. House of Representatives, the lower house of Congress, confirmed the cyber attack in a statement.

The NRCC spokesman Ian Prior said in the statement, "The NRCC can confirm that it was the victim of a cyber intrusion by an unknown entity. The cybersecurity of the Committee's data is paramount, and upon learning of the intrusion, the NRCC immediately launched an internal investigation and notified the FBI, which is now investigating the matter."

According to senior party officials quoted in the report, the NRCC kept the details of the hacking under wrap, hiding it from the party's leadership, as well as its house members.

The officials said that NRCC feared making the details public as it could make it harder to find the attackers.

Further, sources quoted in the report said that hackers had stolen passwords to access some NRCC email accounts and that the hacking was relatively unsophisticated.

The NRCC has refused to release any further details of the hack, with the spokesperson saying, "To protect the integrity of that investigation, the NRCC will offer no further comment on the incident."

However, the report claimed that the NRCC quickly fixed the problem by changing the passwords on accounts at its web-based email provider.

The committee was further said to have taken steps to protect the organization from similar attacks.